Dissection and Anatomy of the Frog (1964)

of the phum vertebrata the vertebrae there is a class called amphibia word amphibia means double life and the animals in this class are the ones which live part of their lives usually the earlier part in water and part on land in all amphibian work even though anesthesia is used it is an extremely good practice to render the animal senseless to pain this is done by destroying both the brain and spinal cord the process is known as pithing if one goes down the mid skull a depression is felt at which point a dissecting needle can be inserted and passed down the length of the spinal column destroys the spinal col destroy other organs has no sense of suppose now we take a look at the gut cavity and its contents in doing this you'll first make a slit through the skin using a pair of blunt scissors and cutting all the way up past the breast bone having done this one the muscles which form a rather nice band at the mid vental line again make a Nick into the muscle mass and carry the slit following the same line that you did when you cut through the skin and you do have to cut through the breast bone which you just heard if at this point one grasps the two cut ends of the breast bone and pulls outward again your best dissection instrument are your fingers you can pin the animal down in this position making it very easy to work on the internal organs notice the heart beating rather actively one can even at this point see that there are two separate areas in the heart two atria and one large ventricle the large structure coming out of the ventricle is the conus arteriosis the main artery leaving the heart rather than pursue a dissection of the blood vessel system at this point let's defer that until after we've examined the organs in the gut cavity the liver the largest gland in the body is composed of three loads and surprising though it may seem this large black sack is the gallbladder in some specimens the gallbladder may appear green these thin wall sacks directly behind the liver found on both sides of the animal are the lungs in order to look further we'll have to enlarge the original cut practically down to the pubis and we should make two side slits to completely expose the viscera we saw the liver earlier and if we remove it from the field of view you see a large muscular organ the stomach and up in this corner the attachment of the stomach to the esophagus the stomach leads to the dadum the first part of the small intestine which is somewhat coiled although not as much as in man and finally leads into the large intestine and I think you can see the difference in size small intestine large intestine and this ultimately empties into the CLA from which wastes are excreted if you look at this movement this is a normal which moves food along the digestive tract you'll notice also by this time that the frog has ceased to live and if we move the liver out of the way we should be able to explore now some of the other organs in the gut cavity between the curvature of the stomach and the duodenum lies a gland which is essential for digestion the pancreas this is best seen from the underside notice this yellowish structure the pancreas notice also that there is a thin tissue throughout the entire digestive tract this is the mesentary and the mesentary suspends the entire contents all of the Digest of organs from the back body wall in the mesentary one also finds this small dark brownish red organ the spleen whose function is the production and destruction of blood cells looking a little deeper into the abdominal cavity one notices some large finger-like projections these are fat bodies they are inter associated with the reproductive organs and this being a male frog the reproductive organs are testes one and the other one looking very closely at the testies they are connected to the kidneys by very fine ducts the Vasa efferentia and it is from the testes through these ducts that the sperm pass on their way to the kidney let's see if we can get a better look at this kidney well here's the left kidney a large dark brown mass and this lighter yellowish area which is just barely visible is the adrenal gland from the base of the kidney is a stout tube the Ura through which both urine and sperm pass to the CLA for comparison let's take a look at the female frog first a preserved one showing a huge number of eggs in the body cavity should you get one of these as a dissection specimen you'll have to remove all of the eggs before you can see any of the internal organs looking now to a frog still a female which has already laid her eggs we can see the these large yellowish masses and the associated fat bodies when the eggs are shed in the body cavity they travel down this fine tube the UCT which terminates in the U a very thinly branched organ that empties into the cloa it's of interest to point out that in the Frog the urine passes first to the CLA then to the urinary bladder this large flabby structure since there's no urine in it at this time and upon contraction of the urinary bladder the urine goes back to the CLA and is excreted from the organism at this point we should take a look at the circulatory system of the Frog and we're switching to a preserved specimen in which the arteries have been injected red for better visualization this will probably be a rather long deection because one must be very careful in dissecting the conus arteriosis as it leaves The ventricle it's possible to see that this branches into three smaller arteries the first of these goes toward the head therefore it must be the cored the second curves and goes deep behind the heart and appears to go down toward the stomach along the back wall this must be the systemic branch and the third branch immediately Forks One Branch goes to the lung the other to the skin in in this area that must be the pulmocutaneous this is the point at which we left off a consideration of the systemic notice that it travels against the back body wall joining the right systemic sending off a branch to the mesenteries and intestines and behind the kidney becoming the dorsal aota with these renal branches coming off if we follow this down a little further practically to the bottom of the body cavity you'll notice the branching of the dorsal aota to the iliacs looking to the veins which are rather collapsed in the specimen we can easily see the left precaver the right precaver the post caver and the Triangular sinus phosis the central nervous system is divided into the brain the spinal cord and the nerves branching from the cord to reach the system one must first remove the skin along the midline of the back and the skin is tough in this region clear up past the eyes having done that you can see a depression which corresponds to the spinal column if one slices at this point and don't worry you're not going to go through the bone but be careful when you use a scal trying not to cut quite toward yourself one should at this point be able to rip out this muscle mass and this is a blunt dissection a little scraping with a scalpel and even though I'm scraping toward myself the blade is pointed away from my thumb brings us down to the level of the spinal C now there is no sense in starting an exposure of the spinal cord down here one may start in the mid region with an old pair of scissors that must be relatively strong Begin by inserting into space between two of the vertebra or bones which go to make up the column snip away and with a pair of forceps lift the bone and attached muscle this is a rather long and tedious process so let's take one frog that has already been toyle the brain in spinal cord the brain is in this region this is the spinal cord we've now finished our generalized dection of the Frog there are many specialized techniques which we won't go into now but regardless of the type of deection that's done one should always Upon finishing make sure to clean his instruments well for